1. Field of the Invention
This invention relates generally to archery bows and more particularly, to improved means for adjusting the angular position or timing of the pulleys in compound bows.
2. Discussion of the Related Art
Compound archery bows have become increasingly popular for hunting and target shooting in recent years. These bows use tension cables which extend over eccentric pulleys rotatably mounted to the bow limbs to provide a mechanical advantage during the drawback and release of a bowstring.
The compound bow includes a bowstring for reception of the arrow. A pair of tension cable portions are connected to the ends of the bow and extend over the eccentrically mounted pulleys. The tension cables typically cross one another between the limbs and attach to the bow limb opposite the pulley over which the respective tension cable extends. As the bowstring is being drawn, the draw weight or force applied to the bow increases to a maximum draw weight and reduces to a lower draw weight at the full draw position due to the eccentric mounting of the pulleys. Accordingly, when the bowstring is in the fully drawn position, maximum potential energy is stored in the bow while the force required to maintain the bowstring in the fully drawn position is less than the maximum draw weight of the bow. In other words, maximum energy is stored in the limbs without requiring maximum force to be applied to the bowstring to hold it at the fully drawn position. This permits the archer to maintain aim on his target prior to release for a longer time and without undue strain for producing a better shot.
The shape of the pulleys determines the draw length of the bowstring. Much inventive energy has been devoted to devices which allow an archer to change the draw length of the bowstring. U.S. Pat. No. 4,774,927 to Larson discloses a pulley having a rotatable member attached thereto which, when rotated, allows for the archer to select one of several draw lengths. This device, however, does not affect the angular position of the pulleys (also referred to as the timing of the pulleys) relative to one another. Due to variations in manufacturing and assembly, the tension cables are not always of identical or optimal length. As a result, the pulleys to which they are attached are either advanced or retarded relative to each other. The solution to this problem is to change the effective cable length of one or both cables. This adjusts the angular positions of the pulleys either advancing or retarding them so that the upper and lower pulleys rotate in unison, reaching peak draw height and let-off portions of the pulleys simultaneously. Many devices have been developed for adjusting the angular position or timing of the pulleys of the bow. All of these methods include devices mounted on the tension cables, between the ends of the limbs. For example one method secures the inside cables to the bow limbs by means of a yoke member which in turn is secured by a yoke cable to the axle upon which the respective eccentric pulley is rotatably mounted.
One prior art patent, U.S. Pat. No. 4,440,142 to Simonds, discloses a yoke cable connected at both its ends to a pulley axle which rotatably supports an eccentrically mounted pulley. The cable extends about a perimetric edge portion of a disk-like yoke for securing the disk relative to the axle. A plurality of attachment grooves are formed in the disk which are disposed at varying distances from the disk center. An end of the tension cable extends through the center of the disk and is received by any one of these attachment portions, and is looped back to itself and fixedly secured by a clasp or sleeve-like member. Such an anchoring device enables the tension in the tension cable to be adjusted by changing which of the attachment portions in which the loop in the tension cable is received.
Such a yoke structure is not without drawbacks. For example, to change the tension cable to a different attachment portion in the disk, tension in the cable must be released to enable the cable to be removed from the existing attachment portion. Additionally, each of the attachment portions is set at some fixed distance from the center which enables only a small number of specific finite tension adjustments to be made with a given disk. Also, by placing an anchoring device on the cable (between the pulleys) the weight of the anchoring device causes oscillation of the cables during movement of the bowstring. This can decrease the accuracy of the bow.
With the instant arrangement, one can change the angular relationship of one pulley with respect to the other or one can change the angular position of both pulleys in an incremental manner. Also, because the adjustment device is mounted on the pulleys, instead of the cables, oscillation of the bowstring is eliminated.